(???????)Boosting antioxidation efficiency of nonstoichiometric CeOx nanoparticles via surface passivation toward robust polymer electrolyte membrane fuel cells

Nonstoichiometric cerium oxide (CeOx) nanomaterials are considered the most efficient radical scavengers with regenerative redox behavior and are emerging as a pivotal ingredient to secure long-lasting energy conversion devices. However, the environment of energy conversion reactions, which hampers a regeneration of Ce chemical states and severely degrades CeOx antioxidation efficiency, engenders the thirst for CeOx surface passivation strategies that confer high colloidal stability, robust chemical durability, and efficient radical scavenging performance. Here, as a proof-of-concept study, we suggest that chemically durable mesoporous silica (mSiO2) shells with high colloidal stability in polar media boost CeOx antioxidation efficiency. The mSiO(2) enabled the even dispersion of the CeOx nanoparticles (NPs) in polar media, effectively mitigated radical scavenging activity degradation, and an increased ratio of highly active Ce(III) states. Importantly, a proton exchange membrane (PEM) based on the CeOx/mSiO(2) core/shell exhibited a much lower disintegration rate during the Fenton's test than the CeOx-based PEM and the pristine one. Furthermore, in fuel cell tests, the CeOx/mSiO(2)-based PEM demonstrated excellent durability preserving 91.7% of initial maximum power density after 100 h-durability tests, while other PEMs underwent drastic performance degradation. In addition, systematic modulation of structural factors in CeOx/mSiO2 allowed demonstrating the multifunctionality of the mSiO2 shell.